Batch processing for semiconductor wafers to form aluminum nitride and titanium aluminum nitride

ABSTRACT

A process used during the formation of a semiconductor device comprises the steps of placing a plurality of semiconductor wafers each having a surface into a chamber of a batch wafer processor such as a diffusion furnace. The wafers are heated to a temperature of between about 300° C. and about 550° C. With the wafers in the chamber, at least one of ammonia and hydrazine is introduced into the chamber, then a precursor comprising trimethylethylenediamine tris(dimethylamino)titanium and/or triethylaluminum is introduced into the chamber. In the chamber, a layer comprising aluminum nitride is simultaneously formed over the surface of each wafer. The inventive process allows for the formation of aluminum nitride or titanium aluminum nitride over the surface of a plurality of wafers simultaneously. A subsequent anneal of the aluminum nitride layer or the titanium aluminum nitride layer can be performed in situ.

FIELD OF THE INVENTION

This invention relates to the field of semiconductor assembly, and moreparticularly to a method for forming a material comprising at least oneof aluminum nitride and titanium aluminum nitride over the surface of aplurality of semiconductor wafers.

BACKGROUND OF THE INVENTION

In the manufacture of semiconductor devices various uses for aluminumnitride (AlN) and titanium aluminum nitride (TiAlN) have been proposed.AlN has been used, for example, as an insulator and as a heat sink.TiAlN has been used for an adhesion layer and as a conductive layer, andboth AlN and TiAlN have been used for diffusion barriers. Aluminumnitride compounds are extremely hard substances thereby making them alsouseful as etch stop layers.

U.S. Pat. No. 5,783,483 describes a method of forming an aluminumnitride layer by first depositing a thin aluminum layer by sputtering,chemical vapor deposition (CVD) or ion implantation. Next, the aluminumlayer is thermally cycled in a nitrogen ambient to form an aluminumnitride barrier layer. An aluminum nitride layer can further be formedin a single step using CVD or reactive sputtering. After formation of adesired layer, aluminum nitride can be patterned using Cl₂ or BCl₃ gasusing reactive ion etching (RIE).

U.S. Pat. No. 5,687,112 describes that titanium aluminum nitride may bedeposited by such methods as physical vapor deposition includingevaporation, ion plating as well as by DC and RF sputtering deposition,chemical vapor deposition, and plasma assisted chemical vapordeposition. The exact method used depends upon many factors, for exampledeposition temperature constraints imposed by the composition of thetarget material.

Prior methods of forming TiAlN and AlN include formation of the materialon a single wafer. Single wafer processing is known to be time consumingand therefore expensive, but a process to form a layer of TiAlN or AlNsimultaneously over a plurality of wafers has not been feasible as priorprecursor technology has not been viable with only thermaldecomposition. In addition to costs added from long processing times,single wafer processing is expensive because additional equipment mustbe purchased to provide adequate manufacturing throughput. Further,previous methods of forming AlN or TiAlN result in layers having varyingthickness over device features, for example thinning at the edges offeatures, which can decrease device performance and yields. A method forforming TiAlN and AlN on two or more wafers simultaneously which alsocan improve step coverage would increase production throughput, decreasecosts, and improve device performance and yields, and would therefore bedesirable.

SUMMARY OF THE INVENTION

The present invention provides a new process for forming a layercomprising one of aluminum nitride and titanium aluminum nitride over asemiconductor substrate assembly. The process decreases the time andcost of wafer manufacture and increases wafer throughput by allowing forthe simultaneous processing of multiple wafers. In accordance with oneembodiment of the invention, at least two wafers are placed into adiffusion furnace. With the wafers in the furnace, a precursorcomprising at least one of triethylaluminum and trimethylethylenediaminetris(dimethylamino)titanium is placed into the diffusion furnace. Thetemperature of the wafers is increased and a layer comprising at leastone of aluminum nitride and titanium aluminum nitride is simultaneouslyformed over a surface of each wafer.

Thus the instant process allows for the formation of a layer comprisingone of a titanium aluminum nitride layer and an aluminum nitride layerover the surfaces of two or more wafers simultaneously therebyincreasing throughput over conventional single wafer processing.

Other objects and advantages will become apparent to those skilled inthe art from the following detailed description read in conjunction withthe appended claims and the drawings attached hereto.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross section depicting a wafer substrate assembly and acapacitor bottom electrode layer which can be formed using an embodimentof the invention;

FIG. 2 is a cross section depicting the structure of FIG. 1 afterforming various other layers, one or more of which can be formed usingan embodiment of the inventive process; and

FIG. 3 is a cross section depicting the use of an aluminum nitride layeras a dielectric to protect and to improve the electrical characteristicsof a field emitter display tip.

It should be emphasized that the drawings herein may not be to exactscale and are schematic representations. The drawings are not intendedto portray the specific parameters, materials, particular uses, or thestructural details of the invention, which can be determined by one ofskill in the art by examination of the information herein.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The instant invention comprises the formation of one or more layers ofeither aluminum nitride (AlN), titanium aluminum nitride (TiAlN), or oneor more layers of both materials over a plurality of waferssimultaneously using an inventive process. While it is appreciated thatAlN is a dielectric and TiAlN is a conductor, the layers are formedusing similar processes with a common precursor for each material, andan additional precursor to form TiAlN.

A first inventive embodiment to form an aluminum nitride dielectricincludes placing a plurality of wafers (at least two wafers andpreferably a larger number) into a diffusion furnace reactor. A furnaceincluding a dispersion injector, such as a model A400 vertical diffusionfurnace available from ASM of Phoenix, Ariz., as well as othermultiple-wafer furnaces, would be sufficient.

After the wafers are placed in the furnace, a furnace purge, for exampleusing one or both of N₂ and argon, can be performed to provide acontrolled process atmosphere. Next, the wafers are heated to atemperature of between about 350° C. and about 550° C., and preferablyin the range of about 425° C. to about 450° C. in the presence of aninert gas such as argon. Once the target temperature is reached, ammoniais bottom injected into the reactor at a gas flow rate of from about 5standard cm³/minute (sccm) to about 300 sccm to provide an ambientammonia atmosphere for each wafer. It should be noted that it may bepossible to use hydrazine for this step to provide a hydrazineatmosphere, and for other processing steps, rather than ammonia.Subsequently, a flow of an aluminum precursor such as triethylaluminum(TEAL) is initiated, for example at a flow rate of 300 sccm or less. Theflow of TEAL is maintained for between about 300 seconds (5 minutes) andabout 10,000 seconds (2.78 hours), and preferably for between about 500seconds and 1500 seconds to form an aluminum nitride layer of from about25 angstroms (Å) to about 2.0K Å thick. Pressure for the above steps ismaintained at about one torr or less. Thicker films may be deposited byincreasing the deposition time. Finally, the wafer is cooled and waferprocessing is continued, or an optional in situ anneal step can beperformed at temperature. This process results in an AlN dielectriclayer formed simultaneously over the surfaces of a plurality of wafers,thereby decreasing processing time over a single-wafer process.

To form a layer of titanium aluminum nitride, a similar process is used.The reactor parameters remain the same as those used for the formationof aluminum nitride, but the chemistry is altered. To form TiAlN, bothammonia and hydrogen are bottom injected into the reactor at a gas flowrate of about 500 sccm or less. Further, both TEAL and an a titaniumprecursor such as trimethylethylenediamine tris(dimethylamino)titanium(TMEDT) are bottom injected at temperature in the presence of ammonia asdescribed for AlN formation. Gas flow rates of 500 sccm or less for boththe TEAL and TMEDT would be sufficient, and a duration of between about100 seconds and about 10,000 seconds, and preferably for between about500 second and 1500 seconds would form a titanium aluminum nitride layerfrom about 25 Å to about 2K Å thick. For TiAlN formation, a pressure ofless than one torr is maintained.

It should be noted that the above flow rates are batch size dependent.For large batches, the flow rates may need to be increased, for exampleup to 1,000 sccm. The flow rates required can be determined by anartisan of ordinary skill from the information contained herein. Tofurther increase the number of wafers which can be simultaneouslyprocessed, a multiport injection of the TEAL and/or TMEDT up the lengthof the tube can be performed. The multiport injection, in addition toallowing for increased load size, may improve uniformity of the layeracross the batch of wafers.

After the formation of the TiAlN film, an in situ anneal or conditioningstep may be required in some cases, for example to densify the film toprevent the unbonded titanium from oxidizing upon exposure to air.Additionally, more than one deposition step and more than one annealstep may be used to achieve a more stable film. An anneal step, forexample using NH₃, N₂, or H₂ at the deposition temperature or higherbetween 200 millitorr and 25 atmospheres, for example at one atmosphere,would cause the unbonded titanium within the film to bond with nitrogento form a densified TiAlN film. Thus the instant process for formingTiAlN allows the formation of the material over a plurality of wafersubstrates simultaneously, and also decreases processing time resultingfrom a subsequent in situ conditioning or anneal step in the diffusionfurnace.

FIGS. 1 and 2 illustrate one possible use of the inventive process toform a layer of TiAlN as a capacitor bottom electrode and another layeras a top plate, and to form a layer of AlN as a capacitor dielectric andanother layer as a deposited antireflective coating (DARC) layer under aphotoresist layer. This process is for purposes of illustration only, asthe inventive process can be used to form either TiAlN or AlN, or both,for any particular structure for which the material is useful.

FIG. 1 depicts a semiconductor substrate assembly comprising asemiconductor wafer 10 having doped regions therein 12, field oxide 14,gate oxide 16, and a plurality of transistor gates 18 having aprotective oxide cap 20 such as tetraethyl orthosilicate thereover andoxide or nitride spacers 22. This structure can be manufactured by oneof ordinary skill in the art.

Next, a plurality of wafers comprising the wafer substrate assemblydescribed above are placed into a diffusion furnace. The wafers areheated to a temperature of from between about 350° C. to about 550° C.,for example to about 425° C. in an argon, hydrogen, or nitrogenatmosphere. Once the wafers reach 425° C. ammonia and hydrogen arebottom injected into the reactor at a gas flow rate of 500 sccm or less,for example 290 sccm for each gas to provide an ammonia atmosphere.Subsequently, a flow of TEAL and TMEDT are bottom injected into thereactor at 290 sccm for each gas. Using these parameters, it is expectedthat TiAlN will form on the wafer substrate assembly surface such asthat depicted in FIG. 1 at a rate of about 10 Å/minute, and thus for atarget of about 500 Å this process is continued for 50 minutes to formthe TiAlN layer 24 as depicted in FIG. 1.

Next, a planar layer such as a borophosphosilicate glass (BPSG) layer 26and a patterned photoresist layer 28 are conventionally formed over eachwafer as depicted in FIG. 1 which requires removal of the wafers fromthe furnace. The exposed BPSG and TiAlN materials are then removed toexpose the wafers at the locations uncovered by resist. This etchexposes the wafer at various doped regions, for example at region 30where a digit line contact will be formed. The etch further defines thestorage capacitor bottom electrode (40 in FIG. 2). The resist and BPSGare stripped using conventional processing subsequent to forming theFIG. 1 structure.

Next, the wafers are placed back into the furnace to form the capacitorcell dielectric and the top plate. A cell dielectric may be formed fromAlN using an inventive process, for example by heating the wafers to atemperature of from between about 350° C. to about 550° C., for exampleto about 425° C. in an argon atmosphere. Once the wafers reach 425° C.,ammonia is bottom injected into the reactor at a gas flow rate of 300sccm or less, for example at 290 sccm, to provide an ammonia atmosphere.Subsequently, a flow of TEAL is bottom injected into the reactor at 290sccm. Using these parameters, it is expected that AlN will form on awafer substrate assembly surface such as that depicted in FIG. 2 at arate of about 240 Å/minute (about 4 Å/sec), and thus for a target offrom about 50 Å to about 250 Å this process is continued for betweenabout 12 seconds to about one minute to form the AlN layer 42 asdepicted in FIG. 2.

Subsequently, another layer of TiAlN 44 can be formed conformally withthe cell dielectric 42 to form the capacitor top plate. The processdescribed above using TEAL and TMEDT as precursors can be modified toform a desired layer of from about 300 Å to about 500 Å thick.

The wafers are then removed from the furnace and a planar layer of BPSG46 is formed according to means known in the art. FIG. 2 further depictsan AlN antireflective layer 48 formed over the BPSG layer using aprocess described above to form AlN. Using the parameters describedabove for forming a cell dielectric layer, it is expected that anantireflective AlN layer will form over BPSG at a rate of about 240Å/minute (4 Å/sec). The thickness of the AlN antireflective layer willdepend on the qualities of the material, and a layer of from about 100 Åto about 500 Å, for example 300 Å thick should be sufficient. Subsequentto forming the antireflective layer 48 a patterned resist layer 50 isformed. The material overlying the wafer is etched to expose the waferat the digit line contact area 30. Wafer processing continues to form asemiconductor device.

Another possible use of the invention is depicted in FIG. 3 whichincludes an array of emitter tips 60 such as those used in a fieldemitter display (FED). The tips are formed according to means known inthe art on a plurality of substrate assemblies such as siliconsemiconductor wafers having various layer formed therein and thereover,or other substrate assemblies, one of which is depicted as element 62. Alayer of aluminum nitride dielectric 64 is formed simultaneously overthe tips on the plurality of wafer substrate assemblies using equipmentsettings as described above. Aluminum nitride reduces the effective workfunction of the field emitter tips thereby reducing the requiredoperating voltage. An aluminum nitride coating also provides stabilityagainst degradation from contaminants and oxidation. For a field emittertip having a height of one micron, a layer of AlN about 50 Å to about500 Å thick should be sufficient to provide the necessarycharacteristics. The thickness of the layer is dependent on thesharpness of the tip, the material from which the tip is formed, and theporosity of the tip material.

In some uses of the invention it may be desirable to decrease the etchrate of the AlN and/or TiAlN material when etching surrounding materialssuch as oxide and nitride, for example in processes which use the AlN orTiAlN as a mask. This can be accomplished by doping the TiAlN or AlNwith carbon, for example to a concentration of less than 0.1%, byproviding a carbon-containing gas in the chamber during formation of thefilm. Suitable carbon-containing gasses include CH₄, CO₂, acetylene, andethylene, and other similar materials. It should be noted that C0 ₂ maybe inadequate for this step as it could possibly incorporate O₂ into thefilm. Further, lowering the NH₃ during the film deposition mayincorporate sufficient carbon into the film using the organometallicprecursor itself as a carbon source.

The instant invention allows the formation of an aluminum nitride layeror a titanium aluminum layer simultaneously over a plurality of wafers.The invention further allows for the conditioning or annealing of analuminum nitride layer or a titanium aluminum nitride layer during oneor more anneals over a plurality of wafers in situ which is a morecost-effective process than single-wafer processing. To increasethroughput, a fast-ramp furnace can be utilized to bring the wafers totemperature at a rate of as high as 750° C./minute (for example about700° C./minute) without excess thermal budget. Thus a rapid ramp to ananneal temperature of greater than about 800° C. then a decrease intemperature to ambient can be advantageously implemented.

While this invention has been described with reference to illustrativeembodiments, this description is not meant to be construed in a limitingsense. Various modifications of the illustrative embodiments, as well asadditional embodiments of the invention, will be apparent to personsskilled in the art upon reference to this description. For example, theinventive process can be used to form only one of a bottom electrode, acell dielectric, a top plate, and an antireflective layer, or otherconductive and dielectric structures can be formed using the inventiveprocess. Further, an aluminum precursor other than TEAL and a titaniumprecursor other than TMEDT can be used. Generally an aluminum precursorin the form of R₃Al can be used to form AlN and it should be recognizedthat the aluminum precursor is not restricted to the use of therecommended R₃Al precursor TEAL. A titanium precursor such astetrakisdimethylaminotitanium (TDMAT) or tetrakisdiethylaminotitanium(TDEAT) may function adequately. It is therefore contemplated that theappended claims will cover any such modifications or embodiments as fallwithin the scope of the invention.

What is claimed is:
 1. A process used to form a film comprising aluminumnitride comprising the following steps: placing at least two wafers intoa diffusion furnace; increasing a temperature of said wafers in saiddiffusion furnace; with said wafers in said furnace, introducing analuminum nitride precursor into said diffusion furnace; and in saidfurnace, forming a layer comprising aluminum nitride from said aluminumnitride precursor over a surface of each wafer.
 2. The process of claim1 wherein said step of introducing said precursor comprises introducinga compound in the form R₃Al.
 3. The process of claim 2 wherein said stepof introducing said precursor comprises introducing a materialcomprising triethylaluminum.
 4. The process of claim 3 wherein said stepof introducing said precursor further comprises introducing at least oneof trimethylethylenediamine tris(dimethylamino)titanium,tetrakisdiethylaminotitanium, and tetrakisdimethylaminotitanium, andsaid step of forming said layer comprising aluminum nitride comprisesforming a titanium aluminum nitride containing film.
 5. The process ofclaim 1 further comprising the step of introducing at least one ofammonia and hydrazine into said furnace subsequent to said step ofplacing said at least two wafers in said furnace and prior to said stepof introducing said precursor into said furnace.
 6. The process of claim1 wherein said step of increasing said temperature of said wafers insaid diffusion furnace comprises increasing said temperature to betweenabout 300° C. and about 550° C.
 7. A process used during the formationof a semiconductor device comprising the following steps: placing aplurality of semiconductor wafers each having a surface into a chamber;heating said wafers to a temperature of between about 300° C. and about550° C.; with said wafers in said chamber, introducing at least one ofammonia and hydrazine into said chamber; with said wafers in saidchamber, introducing an aluminum nitride precursor into said chamber;and in said chamber, simultaneously forming a layer comprising aluminumnitride over said surface of each said wafer.
 8. The process of claim 7wherein said step of introducing said precursor comprises introducing acompound in the form R₃Al.
 9. The process of claim 8 wherein said stepof introducing said precursor introduces a compound comprisingtriethylaluminum.
 10. The process of claim 9 wherein said step ofintroducing said precursor further comprises introducing at least one oftrimethylethylenediamine tris(dimethylamino)titanium,tetrakisdiethylaminotitanium, and tetrakisdimethylaminotitanium, andsaid step of forming said layer comprising aluminum nitride comprisesforming titanium aluminum nitride over the surface of each said wafer.11. The process of claim 10 further comprising the step ofphoto-defining a capacitor bottom electrode from said titanium aluminumnitride layer.
 12. A process used to form an electronic device having afilm comprising aluminum nitride, the process comprising the followingsteps: placing at least two wafers into a diffusion furnace; increasinga temperature of said wafers in said diffusion furnace to a depositiontemperature; with said wafers in said furnace, introducing an aluminumnitride precursor into said diffusion furnace; in said furnace at aboutsaid deposition temperature, forming a layer comprising aluminum nitridefrom said aluminum nitride precursor over a surface of each wafer; andsubsequent to said step of forming said layer comprising aluminumnitride, annealing said layer at a temperature equal to or greater thansaid deposition temperature in an atmosphere comprising at least one ofH₂, N₂, and NH₃ at a pressure of between about 200 millitorr and 25atmospheres.
 13. The process of claim 12 further comprising the step ofintroducing a carbon-containing gas into said diffusion furnace duringsaid step of introducing said aluminum nitride precursor into saiddiffusion furnace.
 14. The process of claim 13 wherein said step ofintroducing said carbon-containing gas into said diffusion furnacecomprises introducing at least one of CH₄, CO₂, acetylene, and ethylene.15. The process of claim 12 wherein said step of forming said layercomprising aluminum nitride is a first deposition step an d forms afirst layer comprising aluminum nitride layer and said step of annealingis a first anneal step, further comprising the following steps:subsequent to said first anneal step, with said wafers in said furnace,introducing an aluminum nitride precursor into said diffusion furnace;in said furnace at about said deposition temperature, forming a secondlayer comprising aluminum nitride from said aluminum nitride precursorover a surface of each wafer; subsequent to said step of forming saidsecond layer comprising aluminum nitride, annealing said first andsecond layers at a temperature equal to or greater than said depositiontemperature in an atmosphere comprising at least one of H₂, N₂, and NH₃at a pressure of between about 200 millitorr and 25 atmospheres.
 16. Theprocess of claim 15 wherein said step of forming said second layercomprises forming said second layer such that it contacts said firstlayer.
 17. The process of claim 12 further comprising the step ofpurging said diffusion furnace using at least one of N₂ and argon priorto said step of introducing said aluminum nitride precursor into saiddiffusion furnace.
 18. The method of claim 12 wherein said anneal stepincludes the step of ramping said furnace to an anneal temperature at arate of at least 700° C./minute.
 19. The process of claim 12 whereinsaid anneal step comprises increasing said temperature to a depositiontemperature of between about 300° C. and about 500° C.
 20. A processused to form a conductive layer comprising titanium aluminum nitridecomprising the following steps: placing at least two wafers into adiffusion furnace; increasing a temperature of said wafers in saiddiffusion furnace; with said wafers in said furnace, introducing aprecursor comprising at least one of trimethylethylenediaminetris(dimethylamino)titanium, tetrakisdiethylaminotitanium, andtetrakisdimethylaminotitanium into said diffusion furnace; and in saidfurnace, forming a layer comprising titanium aluminum nitride from saidprecursor over a surface of each wafer.
 21. The process of claim 20wherein said step of introducing said precursor further introducestriethylaluminum.
 22. The process of claim 20 further comprising thestep of introducing both ammonia and hydrazine into said furnacesubsequent to said step of placing said at least two wafers in saidfurnace and prior to said step of introducing said precursor into saidfurnace.
 23. The process of claim 20 further comprising the step ofproviding a carbon-containing gas in said diffusion furnace during saidstep of forming said layer comprising titanium aluminum nitride.
 24. Theprocess of claim 23 further comprising the step of doping said layercomprising titanium aluminum nitride with carbon to a concentration ofless than 0.1% carbon during said step of forming said layer comprisingtitanium aluminum nitride.
 25. The process of claim 20 furthercomprising the step of photo-defining a capacitor bottom electrode fromsaid layer comprising titanium aluminum nitride.
 26. The process ofclaim 20 further comprising the following steps: with said wafers insaid furnace, introducing a precursor comprising triethylaluminum intosaid diffusion furnace; and in said furnace, forming an aluminum nitridelayer from said aluminum nitride precursor over a surface of each wafer.